Method of starting up a dehydrogenation process



Nov. 3, 1959 w. J. L. KEARNS METHOD OF STARTING UP A DEHYDROGENATION PROCESS Filed April 25, 1956 United States Patent signor to Polymer Corporation Limited, Sarnia, 0ntario, Canada, 'a corporation of Canada Application April 23, 1956, Serial No. 579,793

4 Claims. (Cl. 260-680) This invention relates to a process for the dehydrogenation of olefinic hydrocarbons, particularly. monoolefins containing atl'east four carbon atoms in the olefinic chain. More particularly it relates to a'method of commensing the dehydrogenation reaction and still more particularly it relates to a method for the'start-up of the reaction.

In this specification the term start-up is intended to mean those series of steps which serve to raise the tem perature ofthe dehydrogenation catalyst to the normal dehydrogenation temperature.

The catalysts envisaged in the process of the present invention are those which, during the process of their manufacture into the'commercially acceptable form become admixed with a combustible lubricant, which must subsequently be removed. The better-known of such catalysts are those in which the active ingredient is calcium nickel phosphate; The'most widely used catalyst of this type is the calcium nickel phosphate-chromium oxide catalyst disclosed in United States Patent No. 2,442,320 issued May 25, 1948 to Andrew J. Diet-zler et al. This particular catalyst is in the'form of pellets. During the process of the manufacture of such pellets they become admixed with combustible lubricant, 'such as graphite, which must subsequently be removed in order that the dehydrogenation reaction may proceed. p

In order to remove the combustible lubricant fromthe catalyst, it is necessary to heat the catalyst in the presence of steam and a controlled amount of oxygen or oxygencontaining gas, elg. air so that such combustible lubricant burns oil at a sufficiently slow rate that it does not damage the catalyst.

Catalysts of the type used in the present invention for the dehydrogenation of monoolefins conventionally require superheated steam in the process. To avoid wetting the catalyst during start-up, the charged reactors have, in the past, used the followingmethod of start-up;

The charged reactors are warmed above the condensation point of steam by recirculating fuel gas through heaters and then through the catalyst beds. In order that fuel gas and oxygen are not intermixed within explosive limits, the large reactors, furnaces, and connecting equipv ment are usually purged with an inert gas, which is essentially nitrogen and carbon dioxide. This purging operation usually requires as much as 36 hours time during the start-up procedure, since most plants are not capable of producing large quantities of such infrequently used gas. When the oxygen content of the efiluenbis less than about 0.5%, the inert gas is displaced with fuel gas and recirculation is then established between the furnaces and the reactors. When the catalyst beds are heated to a temperature greater than 212 F., preferably 2,91 1,453 Patented Nov. 3, 1959 400-600 F. the circulation of fuel gas is terminated, and superheated steam is added. The steam is passed through the catalyst bed until it reaches a temperature of about 900 to 1150" F. at which time a controlled amount of oxygen or oxygen-containing gas, e.g. air, is added together with the" steam 'for the purpose of oxidizing the carbonaceous material from the catalyst. y 1 The entire'process is lengthy and costly, tfirstly, because of the fact that fuel gas is used to heat the catalyst. Such fuel gas creates a fire hazard in that there is possible furnace damage from tube leakage of fuel gas into the combustion zones. Secondly, because of the amount of inert gas needed to purge the reactors, the purging operation is time consuming.

It is, therefore an-object of the invention to elfect a start-up of 'the dehydrogenation in such'a manner that a minimum of time is wasted.

It isa further object of this invention to provide a safer method of efiecting such start-up.

These and other objects are achieved in the process of commencing a dehydrogenation reaction using new catalyst, in the form of pellets which contain a combustible lubricant in the improvement which comprises effecting such start-up by passing hot air at a maximum temperature of about 600 F. through such catalyst until the minimum temperature of such-catalyst bed is at least slightly higher than the temperature at which steam condenses upon such catalyst. Subsequent heating of the air-heated catalyst to its normal operating temperature includes passing superheated steam through the catalyst in order to heat Such catalyst to the required operating temperature. A controlled amount of air is then admixed with the steam and passed through the catalyst to oxidize said combustible lubricant.

More particularly, the invention resides in the process of efiectingthe start-up of a new calcium nickel phosphate-chrornium oxide catalyst, in the form of pellets which contain graphite, in the improvement which comprises effecting such start-up. by passing hot air through such catalyst until the minimum temperature of the entire catalyst bed is at least-225 F., and, for safety purposes, is .at a maximum temperature of 600 F. Subsequent heating of "the air-heated catalystto its normal operating temperature includes passing superheated steam through such catalyst, in order to heat said catalyst to the required operating temperature. A controlled amount of air is then admixed with the steam and passed through the cat- "alyst in order to oxidize the graphite therefrom.

The minimum and maximum temperatures to which the catalyst bed is heated by means of the hot air only, are subject to slight variations, depending upon the safety factor desired. For example, the minimum temperature is'set by the condition that the presence of free water onthe catalyst is to'ibe avoided. Hence, theoretical con- 'sid erfations would require a minimum temperature of 212 However, in order to avoid the danger that certain areas of the catalyst bed may be at a temperature below the temperature indicated by the thermocouples used to measure thetemperature, it "is advisable to opcrate at a minimum .temperature of 225 F. Similarly, examples to be given below indicate the graphite burns ofi the catalyst-at temperatures greater than 885 F. Nevertheless, it .is theoretically possible for the graphite to ignite at temperature lower than 885 F., and a slight amount of burning would spread uncontrolled over a large amount of catalyst, thereby resulting inmaking unsuitable for the dehydrogenation the catalyst so ignited. Hence, it is advisable to impose a maximum limit on the temperature to which the catalyst is raised by means of the hot air. The maximum temperature contemplated in the present invention is 600 F., but, higher temperatures may be used if so desired. However, at temperatures in excess of 600 F., the higher the temperature, the greater is the danger of uncontrolled combustion of the combustible lubricant on the catalyst.

Pilot plant and commercial scale operations were carried out to determine the optimum temperature for the air start-up procedure.

The Pilot Plant experiments to determine a safe air temperature for purposes of heating up beds of new calcium nickel phosphate-chromium oxide catalyst was divided into two stages; the first stage consisted of four experiments, the first two involving the use of a modified Pilot Plant reactor which cointained approximately 160 lbs. of calcium nickel phosphate-chromium oxide catalyst, whlie the other two experiments were carried out in the normal Pilot Plant isothermal reactor containing approximately 335 grams of calcium nickel phosphatechromium oxide catalyst; the second stage involved the use of larger samples of the calciumnickel phosphatechromium oxide catalyst, using the apparatus shown diagrammatically in Fig; 1. The commercial scale operations were performed in two experiments using the standard amounts of catalyst, and with a flow of air of 18,000 lb./hr.

The first stage of the Pilot Plant experiments consisted of passing preheated 'air through the catalyst beds at increasingly higher temperatures and determining whether any graphite was burned off the catalyst by measuring the carbon dioxide content of the reactor effluent gases. 0

EXAMPLE I The temperature of the heated air passing through a "bed of 160 lbs. of calcium nickel phosphate-chromium oxide catalyst was raised progressively to a maximum of 645 F. During the run, the catalyst pellets at the top of the bed attained a temperature of 585 F. and pellets at a depth of one foot attained a temperature of 482 F. CO analysis on the reactor efiiuent indicated that no graphite was being burned 01f the catalyst. On visual inspection at the end of the run, the catalyst appeared exactly the same as new calcium nickel phosphatechromium oxide catalyst from the same lot.

EXAMPLE II The temperature of the heated air passing through a bed of 169 lbs. of calcium nickel phosphate-chromium oxide catalyst was raised progressively to a maximum of 604 F. During the run, the catalyst pellets at the top of the bed attained a temperature of 596 F. and pellets at a depth of one foot attained a temperature of 541 F.

CO analysis on the reactor efiiuent indicated that no graphite was being burned off the catalyst. On visual inspection at the end of the run, the catalyst appeared exactly the same asjnew calcium nickel phosphate-chromium oxide catalyst from the same lot. Carbon analysis on the experimental calcium nickel phosphate-chromium oxide catalyst and new'calcium nickel phosphate-chromium oxide catalyst revealed no difference in'carbon content. 7

EXAMPLE III phate-chromium oxide catalyst.

4 EXAMPLE IV Air was passed through a 334 gm. bed of calcium nickel phosphate-chromium oxide catalyst which was heated for successive three hour periods to 525 F., 705 F., 885 F., 1065 F. and 1245 F. CO analysis on the reactor effiuent showed a net increase above the temperature of 885 F. indicating that graphite was being burned off the catalyst. On visual inspection at the end of the run, the catalyst appeared completely burned ofi.

These four experiments indicate that the calcium nickel phosphate-chromium oxide catalyst may be preheated in the presence of air to a temperature below 850 F. They show that the graphite on the catalyst starts to burn off at temperatures above 850 F.

For the second stage of the Pilot Plant work, the apparatus shown diagrammatically in the drawing was used.

In the drawing it is seen that the reactor 1 consists of a drum containing a bed of catalyst 2 between upper and lower screens 3. The lower screen also rests upon fire bricks 4. Within the reactor are thermocouples 5, 6 and 7. Thermocouple 5 is for the purpose of measuring the air temperature just above the catalyst. Thermocouple 6 is for the purpose of measuring the catalyst temperature at about 1%" below the surface of the catalyst bed. Thermocouple 7 is for the purpose of measuring the catalyst temperature at a distance of about 10%" below the surface of the catalyst. The various temperatures were recorded using a Braun potentiometer-type multipoint recorder (not shown), range 32 F.-572 F. For temperatures above 572 F., a portable potentiometer box (also not shown) was substituted for the Braun multipoint recorder, and measurements were recorded by the operator. High pressure air is first passed through an air filter 8, through a pressure reducing valve 9 and rotameter 10 to the electric steam superheater 11. It is then passed through a p.s.i. steam heated water evaporator 12, and subsequently to a third preheater 13. It then passes through 1" pipe 14 to the reactor 1, and it is admitted to the reactor by means of a nozzle 15 which consists of 8 /1." holes drilled in a cap which covers the pipe 14 immediately within the reactor 1. Exit air then is passed through coolers 16 and 17. It was found that air temperatures as high as 650 F. were attained at a flowrate of 19.3 s.c.f.m. (calculated at 14.7 p.s.i. absolute and 70 F.). This represented 435 v./hr. per unit volume of catalyst and was the greatest air flow possible without increasing the size of the supply pipe lines. '1. v

During theoperation, measurement of the carbon dioxide content of the air entering and leaving the reactor was'ma'de using the Orsatz caustic bubbler technique.

EXAMPLE V the top of the reactor was 147 F. After 21 hours of operation' eertain changes were made in the air heating system andthe. air temperature attained with an air fiow of 35 v./v./hr.'was 217 F. When it was noticed that a brief reduction in ,air flow, to approximately 20 v./v./hr., was accompanied by a sharp decrease in temperature, the air flow was increased to 50 and then to 65 v./v./hr. and increases noticed in all temperatures. After about 29 hours of operation the experiment was discontinued during aweekend shutdown and the catalyst temperature decreased from F. to 80 -F.

When the experiment was recommenced, irregularities were noticed in the temperature records for the first 30 minutes at ptrst a- This wa thou ht to be due to a surge of very hot air from the furnace which had been heated to I200 F;

The, air rate was increased progressively from 35 v./v./hr. to 65, 87, 110, 140 and 187 v./v./hr. and in- 6 2.2" F. A delay of approximately 1 hour was noticed between the time of rapid temperature increase of the. air and of the top of the catalyst bed. A further delay. of approximately 4 hours elapsed before the lower tem creases were noted in both air and catalyst bed tem- 5 perature point recorded a rapid increase.

peratures. An air temperature of 575 F. was achieved After about 24 hours of operation the air temperature and the catalyst temperature increased to 520 F. at the reached 575 F., the top of the bed 564 F. and the bottop of the reactor and 250 F. at the bottom .of the tom of the bed 520 F. These conditions were mainreactor. Y tained for 16 hours and then the air flow was increased The air rate was still further increased to 355 and then to 435 v./v./hr. The temperatures increased to a maxito 435 v./v./hr. maximum temperature of 650 F. mum of 604 F., 595 F. at the top of the bed and for the air was'observed but it was not possible to main- 540 F. at the bottom of the bed. The run was continued tain this temperature because certain physical limits of for an additional 18 hours at approximately these condithe apparatus used were reached. However, maximum tions. catalyst temperatures of 590 F. at the top of the bed 16 As in the first run the CO measurements were made and 480 F. at the bottom of the. bed were attained and on the air influx and eflux and the analysis indicated maintained for several hours. little, if any, net gain in CO During the course of the experiment, the C0 content When the experiment was discontinued, approximately of the air efiluent was measured at 30 minute intervals 155 lb. of catalyst was recovered and it could not be and was found to vary from nil to 1.7%. Suspicion 20 distinguished from new catalyst. 7 that the high CO readings were not realistic, lead to a Typical data for this example are shown below in check of the CO content of the inlet air. In general Table II. these values were very close, almost within experimental Table II error, to the values for the efliuent air. With each increase in air flow a momentary increase in CO content was observed Air Air Bed Tgrlgpera- Pel'CeEgirCO: in

After an interval of 7 days the experiment was disf g i 7;; g g -r continued and approximately 160 lb. of catalyst rep 7 Top Bottom, In out covered. This catalyst was unchanged in physical appearance. Data, typical of that accumulated during this 355 250 185 153 1.45 1.42 nm shown m Table 355 4.10 345 153 0. 79 1.03 v 355 490 455 252 0. s4 0.55 Table I 355 510 490 400 1. 09 1.45 355 490 430 445 0.33 0.37 355 459 455 445 0.89 0.75 355 480 453 430 0.29 0.31 Bed Tempera- Percent; 002 in 355 555" 537 480 0.23 0.18 Air 1 Air ture air 355 575+ 554 523 nil 0.14 Hours Oper- Flow, Temp., 355 575+ 565 523 0.39 0.44 ation v./v./hr 'F. 5 I 355 575 500 521 0.27 I 0.27 7 Top, Bottom, In Out 435 604 596 507 0.24 0.12 13. F. 435 532 570 541 0.25 0. 44 435 591 1 532 541 0. 45 0. 53 435 588 577 537 0.50 0.55 75 75 435 587 574 535 0.48 0.53 133 104 77 0.11 3; 13 a 3- 173 147 127 nil EXAMPLE VII 7 r 45 Upon completion of the work described above, the Screens, etc. installed in heaters weekend shutdown and addltlonal alf P l' W PY the normal air gradual cling to R heater was restored to ts original servlce. standard 25" tube of calcium nickel phosphate-chromium oxide catalyst (333 gms.) was loaded into the reactor tube and g; 50 heated to 750 F. with air passing through it at 87 400 235 0: 75 v./v./hr. The catalyst was maintained at this tempera- 298 23g ture for three hours and then removed for inspection. 187 508 437 0113 Again, there was no change in the physical appearance 9 7 8 3g of the catalyst. .The percent CO in the air efiluent varied 187 530 475 252 1.68 1. 07 55 from nil to 0.4 during the heating treatment. The weight 3 81%? 8: of catalyst removed was 328 gms. 355 575+ 530 374 0.13 nil The observations for this example are recorded below 355 645 585 442 0.89 0.83 in Table 435 552 532 482 2.03 1.17 435 451 420 450 0. 30 0.30 Table III 435 521 453 392 0.34 0.35 435 571 520 396 0. 22 0.25 0

. Air TAir TBed' Percent 00; in air em 8111 EXAMPLE vr Hours Operation Flow, No.5 No.3. v./v./hr. Thermo, Thermo, In Out The method of Example V was repeated and this time F. F lb. of new calcium nickel phosphate-chromium oxide catalyst was loaded into the drum. Operation was comfig g8 gig menced using the conditions eventually found to be best 120 762 608 I: I: 1 in Example V, i.e., furnace temperatures set to 1200 F. 8 to 1300 and ail flOW at V./V./hl. "120 752 752 0:19 difliculties were again experienced because of overload- 788 752 ing the furnace circuit, the air temperature quickly increased to 500 F. During the initial warming up the maximum rate of temperature increase of the air was EXAMPLE VIII 3.5 F. per minute, the top of the catalyst bed 2.4 F. per minute, and the lower point in the catalyst bed Example VII was repeated under similar conditions. For this example 334 gms. of catalyst was charged to the reactor and with air passing through it at 120 v./v./hr. the bed temperature waselevated for successive 3 hour periods to 525 F.', 705 F., 885 F., 1065 F. and 1245 F. CO measurements were made, as described above, on the air entering and leaving the reactor. At temperatures of 885 F. and above there appeared to be a net increase in the CO present in the air from the reactor varying from 0.2 to 0.8%.

When the catalyst was removed after this experiment, all but approximately 1% of the pellets were completely burned off. The weight of catalyst removed was 324 gms. The typical data for this example are shown below in Table IV.

Table IV Air Bed Percent 001 in air Air Temp. Temp Hours Operation Flow, No. 1 No. 2

v./v./hr. Thermo, Thermo, In Out 120 122 86 nil 120 392 149 nil 120 527 374 1111 120 536 482 nil 120 527 527 nil 120 536 536 0.25 120 717 626 0.19 120 717 707 0.12 120 717 707 nil 120 717 707 nil 120 887 797 nil 120 887 887 0.07 120 887 878 0. l4 0. 16 120 887 887 0. 26 0. 47 120 887 887 0. 42 0. 55 120 l, 067 987 0. 5G 0. 75 120 1, 067 l, 058 0. 54 0.96 120 1, 057 1, 067 0. 69 O. 66 120 1, 067 l, 067 0. 68 0. 79 120 1, 250 l, 202 0.62 0.89 120 1, 250 1, 250 0. 24 0. 84 120 l, 250 1, 250 nil 0.81 120 1, 250 1, 250 0. 17 0. 34 120 1, 250 1, 250 nil nil The next two examples show the improvement when the method of the present invention is applied on a commercial scale.

EXAMPLE IX vThe conventional dehydrogenation unit was loaded with new calcium nickel phosphate-chromium oxide catalyst. Approximately 18,000 lb./ hr. of air was passed through the butene furnace and into the reactors which were operated in parallel. A small amount of air was permitted to back around through the superheaters and was vented at a waste heat boiler. This warmed the steam lines and helped to prevent condensation in the lines when the. steam was finally introduced. The temperature of the air to the reactors was raised to 340 F. in 1 hour and 20 minutes using only one burner on each side of the furnace which was used to heat the air. This temperature was maintained for 7% hours and was then raised to 400 F. in a period of 1 hour and 20 minutes. After 2 hours and 20 minutes at this temperature, every thermocouple in both catalyst beds indicated a temperature greater than 225 F. At this point, the heating was continued with superheated steam from the furnace only. The calcium nickel phosphate-chromium oxide catalyst air start-up was successfully completed in a total elapsed time of 12 /2 hours.

EXAMPLE X The conventional dehydrogenation unit was loaded with new calcium nickel phosphate-chromium oxide catalyst. Air was introduced in the same manner as in Example IX and the temperature of the air to the reactors was raised to 500 F. in 4 hours and 20 minutes. This temperature was maintained for 6 hours and then raised to 520 F. in a period of 40 minutes. After 2 /2 hours at this temperature, every thermocouple in both catalyst beds indicateda .temperature greater than 225 F. The heating was continued with superheated steam from the butene furnace. This calcium nickel phosphate-chromium oxide catalyst air start-up was successfully completed in a total elapsed time of 13 /2 hours.

Thus, using the process of the present invention the fresh calcium nickel phosphate-chromium oxide dehydrogenation catalyst may be ready for dehydrogenation in a period of about 13 hours, whereas the conventional methods result in a time lapse of about 48 hours.

In the process of the present invention it is very important that the temperature be controlled. It was found that, when the minimum temperature of the catalyst bed reaches 225 F. it is possible to use superheated steam instead of the heated air to heat the catalyst bed to its operating temperature and to remove the graphite from the surface of the catalyst pellets by means of heating the catalyst further with such superheated steam and adding a controlled amount of air. While it is, of course, possible to use a higher temperature providing no uncontrolled burning of the graphite occurs and hence possible destruction of the catalyst, the preferred maximum temperature of the inlet air is 600 F. It is desirable to raise the temperature of the air to about 500 F. within the first two hours of the first admission of air, and the temperature should then be regulated to 550- 580 F.

What I claim is: p

1. In the process of commencing a reaction for the dehydrogenation of monoolefins having at least four carbon atoms in the olefinic chain using new calcium nickel phosphate-chromium oxide catalyst in the form of pellets which contain graphite, the improvement which comprises effecting the start-up of such catalyst by passing air at a miximum temperature of about 600 F. through such catalyst until the temperature of the catalyst bed is about 225 -450" F. and subsequently passing superheated steam at a temperature of 400 F.l400 F. and a controlled amount of an oxygen-containing gas through said catalyst in order to oxidize said graphite and to heat said catalyst to the required dehydrogenation temperature.

2. In the process of commencing a reaction for the dehydrogenation of n-butylene to butadiene-l,3 using new calcium nickel phosphate-chromium oxide catalyst in the form of pellets which contain graphite, the improvement which comprises effecting the start-up of such catalyst by passing air at a maximum temperature of about 600 F. through such catalyst until the temperature of the catalyst bed is about 225-450 F., and subsequently passing superheated steam at a temperature of 400-1400 F. and a controlled amount of an oxygen containing gas through said catalyst in order tooxidize such graphite and to heat said catalyst to the required dehydrogenation temperature. 1

3. In the process of commencing a reaction for the dehydrogenation of monoolefins having at least four carbon atoms in the olefinic chain using new calcium nickel phosphate-chromium oxide catalyst in the form of pellets which contain graphite, the improvement which comprises effecting the start-up of such catalyst by passing air at a maximum temperature of about 600 F. through such catalyst until the temperature of the catalyst bed is about 225-450 F., discontinuing the passage of air through said bed, passing superheated steam at a temperature of 400 F .l400 Fjthrough the catalyst bed until the temperature of the bed is about 900-1150 F. and continuing the passage of such steam while adding thereto a controlled amount ofan oxygen-containing gas in order to oxidize said graphite.

4. In the process of commencing a reaction for the dehydrogenation of n-butylene having at least four carbon atoms in the olefinic chain using new calcium nickel phosphate-chromium oxide catalyst in the form of pellets which contain graphite, the improvement which comprises effecting the start-up of such catalyst by passing air at a maximum temperature of about 600 F. through such catalyst until the temperature of the catalyst bed is about 225 450 F., discontinuing the passage of air through said bed, passing superheated steam at a temperature of 400 F.-l400 F. through the catalyst bed until the temperature of the bed is about 9001150 F. and continuing the passage of such steam while adding thereto a controlled amount of an oxygen-containing gas in order to oxidize said graphite.

10 References Cited in the file of this patent UNITED STATES PATENTS Britton et al. May 25, 1948 Pitzer Mar. 27, 1956 OTHER REFERENCES Britton et al. II, Ind. and Engr. Chem, vol. 43 (1951) pp. 2871-2874. 

1. IN THE PROCESS OF COMMENCING A REACTION FOR THE DEHYDROGENATION OF MONOOLEFINS HAVING AT LEAST FOUR CARBON ATOMS IN THE OLEFINIC CHAIN USING NEW CALCIUM NICKEL PHOSPHATE-CHROMIUM OXIDE CATALYST IN THE FORM OF PELLETS WHICH CONTAIN GRAPHITE, THE IMPROVEMENT WHICH COMPRISES EFFECTING THE START-UP OF SUCH CATALYST BY PASSING AIR AT A MIXIMUM TEMPERATURE OF ABOUT 600* F. THROUGH SUCH CATALYST UNTIL THE TEMPERATURE OF THE CATALYST BED IS ABOUT 225* -450* F. AND SUBSEQUENTLY PASSING SUPERHEATED STEAM AT A TEMPERATURE OF 400* F. -1400* F. AND A CONTROLLED AMOUNT OF AN OXYGEN-CONTAINING GAS THROUGH SAID CATALYST IN ORDER TO OXIDZE SAID GRAPHITE AND TO HEAT SAID CATALYST TO THE REQUIRED DEHYDROGENATION TEMPERATURE. 